Rodrigues-Filho, J.L.; Branco, J.O.; Monteiro, H.S.; Verani, J.R., and Barreiros, J.P., 2015. Seasonality of ichthyofauna bycatch in shrimp trawls from different depth strata in the southern Brazilian coast.
Changes in the species composition and ecological descriptors of fish assemblages in terms of abiotic factors such as depth, temperature, salinity, and granulometry were analyzed. Monthly trawls, from October 2003 to September 2004 (30 minutes each) were analyzed in two areas covering an important shrimp fishing site of the Brazilian coast. Results using bifactorial analysis of variance revealed a seasonal variation of environmental variables (p < 0.05), and granulometry analyses showed that the composition of the fishing grounds was similar—mostly sand. A total of 12,613 fish were collected: 7880 in area I and 4733 in area II. The highest values of capture in numerical abundance (catch per unit effort) occurred during winter. Fifty taxa were caught in area I, and 53 taxa were caught in area II. Both values are considered high when compared to previous studies conducted in nearby areas. Sciaenidae was the most speciose family in all samples and in both areas were dominant in number of species (37 species in area I and 42 species in area II). Cynoscion striatus was the most abundant and dominant species in both areas. Estimates of ecological descriptors, such as richness, diversity, and evenness, showed that the ichthyofauna structure was strongly influenced by climatic factors, and all values were more pronounced during fall and winter. The permutational multivariate analysis of variance demonstrated that ichthyofauna species composition differs among seasons. The Student's t test applied a posteriori showed that the community composition differed (significantly) in the following comparisons: spring vs. fall (p < 0.05) and winter vs. summer (p < 0.05). According to similarity percentage analysis, changes in the community structure were mainly correlated with species classified as abundant, which occurred unevenly during the different periods. Our results show that the fish community is influenced by seasonal variations such as salinity and temperature but not by depth or sand grain sizes.